The present invention relates to a pneumatic tire for running on rough terrain, more particularly to a tread structure suitable for a motorcycle tire, composed of blocks capable of increasing the grip and reducing the harshness when cornering.
In general, pneumatic tires for use in off-road vehicles such as motocross bike and rally car are provided with a block-type tread pattern made up of a plurality of blocks to exert a large drive power on soft ground such as sandy area and muddy area.
In order to increase the drive power and improve running performance on rough terrain, it is conceivable to form a recess (c) in the radially outer surface (b) of a block (a) as shown in FIG. 9 and FIG. 10. The recess (c) increases the edges of the block (a) and improves the grip. But, in the peripheral edge portion of the radially outer surface (b), the compressive stress increases and the apparent rigidity of the block (a) is relatively increased in the peripheral edge portion than in the central portion. As a result, in the case of a motorcycle tire, there is such a problem that, when the tire is tilted in order to make a turn, the harshness felt by the rider is emphasized, and further the lightness of handling is deteriorated.